During certain endocrine states, a release of pituitary FSH occurs that is not accompanied by a rise in serum in LH levels. The work described within this application is designed to provide us with an understanding of the mechanisms responsible for this selective FSH release. Female golden hamsters will be sacrificed immediately before and during these serum FSH rises and hypothalami will be tested for changes in luteinizng hormone-releasing hormone (LHRH) content and in vitro LH and FSH release capacity. Preliminary evidence with cation-exchange chromatography has demonstrated the existence of two forms of LHRH within the preoptico-hypothalamus immediately before the estrous rise in serum FSH levels. Thus, an altered form of LHRH may stimulate a release of pituitary FSH at these times. Anterior pituitary glands collected from these animals will be tested for changes in LHRH receptor affinity and number. These studies will determine whether a change in the receptor occurs prior to or during times of selective FSH releases, changes in pituitary FSH concentration, physiochemical structure (by affinity chromatography) and bioactivity will be tested during these times. In addition, specific neurochemicals, electrochemical stimulations and hypothalamic neural transections and changes in exposure to gonadal steroids will be employed to understand the neural mechanisms that govern the synthesis and release of the altered form of LHRH. It is hoped that the information obtained from the above studies will provide us with a clear understanding of the neuroendocrine events that initiate and maintain a selective release of pituitary FSH.